Organic EL display device having separating groove structures between adjacent elements

ABSTRACT

The invention provides an organic EL display device comprising a plurality of organic EL elements each having at least a first electrode, one or more organic layers participating in light emission capability, and a second electrode, the elements being able to be independently electrically operated to emit light, and a groove structure at the boundary between adjacent organic EL elements for isolating at least one of the electrodes between the adjacent organic EL elements. The organic EL display device featuring a greater proportion of light emitting region, higher reliability, a large size of substrate, a more number of elements arrayed in one substrate, and a reduced cost of manufacture is obtained as well as a method for the manufacture thereof.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates to the structure and preparation of an organicelectroluminescent display device (abbreviated as organic EL displaydevice, hereinafter) for use as a display device or light source.

2. Background Art

Display devices which use organic EL elements have the following sortsof advantages over the liquid-crystal displays that currently representthe mainstream in flat panel displays.

1) They are self-emissive, so the viewing angle is wider.

2) Displays only 2-3 mm thick can easily be manufactured.

3) A polarizing plate is not used, so the color of the emitted light isnatural.

4) The broad dynamic range in brightness results in a crisp, vibrantdisplay.

5) They operate over a broad range in temperature.

6) The response rate is at least three orders of magnitude faster thanliquid-crystal displays, easily enabling the display of moving images.

Despite such superiority, the appearance of organic EL display devicesin the market was retarded for the following reason.

In general, organic EL elements include a stack of three thin filmshaving different functions, an electrode in the form of a "transparentconductive film," an "organic layer including a light emitting layer,"and another electrode made of a "metal or alloy having a low workfunction." Difficult problems arose in the manufacture of EL elements,since the "organic layer including a light emitting layer" and "metal oralloy having a low work function" are susceptible to degradation bymoisture and oxygen, and the "organic layer including a light emittinglayer" is readily soluble in solvents and less resistant to heat.Differently stated, in methods using water, organic solvents and heat,once the "organic layer including a light emitting layer" and a layer of"metal or alloy having a low work function" were formed, it wasdifficult to isolate and divide the elements. This means that when it isdesired to manufacture an organic EL display device of an equivalentclass to the currently available display devices realized with liquidcrystal, the full-grown semiconductor manufacturing technology andliquid crystal display manufacturing technology cannot be appliedwithout modification.

Under the circumstances, several techniques capable of separating secondelectrode elements without exposure to the ambient air were devised.With these techniques, it became possible to manufacture highly reliableorganic EL displays.

One exemplary method is disclosed in JP-A 275172/1993, JP-A 258859/1993,U.S. Pat. No. 5,276,380, and U.S. Pat. No. 5,294,869. This methodutilizes the phenomenon that as shown in FIGS. 30, 32 and 33 when walls43 of a height exceeding the thickness of films 45, 46 constructing theorganic EL medium are positioned between display line electrodes to beseparated, and a material 41 for organic EL elements is vacuumevaporated from a direction not orthogonal to a surface of a substrate33, the material 41 is not deposited in the areas shadowed by the walls43.

However, in order to form light emitting lines of an equal width insatisfactory yields, insulators 42 having a greater width than the walls43, called electrically insulative strips or pedestals 42, must beformed below the walls 43 as shown in FIG. 30. The reason is that sincein the vacuum deposition process, the presence of the walls 43 obstructsthe adhesion of an organic film in proximity to the walls 43, astructure without the insulative strips 42 permits short-circuiting tooccur between the first and second electrodes in the proximity of thewalls 43 where the organic film becomes thin. Then the manufacturingyield becomes extremely low with large sized substrates which make itdifficult to improve the thickness uniformity of the organic film.

Inversely, when the insulative strips 42 are formed for the purpose ofincreasing the manufacturing yield, the width of light emitting lines isrestricted by the region where the insulative strips 42 are formed. Thewidth of the insulative strips 42 is designed in accordance with theangle between a metal evaporation source 31 and the substrate 33 and thesize of the substrate 33 itself, as shown in FIG. 31, for example. Moreparticularly, as shown in FIG. 31, for example, if the width of theinsulative strip 42 is narrow, there arises the problem that the widthof light emitting lines varies with the position on the substrate 33because at position A where the angle between metal atoms traveling fromthe metal evaporation source 31 to the substrate 33 and the wall 43 issmall, as shown in FIG. 32, a film is deposited without problems, but atposition B where the angle between metal atoms traveling from the metalevaporation source 31 to the substrate 33 and the wall 43 is large, asshown in FIG. 33, the region shadowed by the wall 43 becomes wider sothat the light emitting region becomes narrower. Accordingly, in orderto produce light emitting lines of equal width over the entire area ofthe substrate, the insulative strips must be given a greater widthincluding a margin. Also a margin of at least 3 μm to 5 μm is necessaryfor the alignment between the insulative strips and the walls whendisplay devices are fabricated on a large sized substrate using analigner of the full exposure type. However, widening the insulativestrips directly incurs a reduction of the light emitting region, whichis disadvantageous in achieving a bright display.

Alternative methods are methods of providing isolation between lightemitting elements by furnishing cavity structures, trench structures orwell structures, and forming light emitting elements in the respectivestructures, as disclosed in JP-A 262998/1996 and 264828/1996.Apparently, these methods give rise to a similar inconvenient problem.

Further, in methods of forming on an electrode insulative walls havinginversely tapered structures, overhang structures or undercut structuresas disclosed in JP-A 315981/1996, 283280/1997, and 161969/1997,insulative strips become necessary in actual practice fromconsiderations to form light emitting lines of an equal width in goodyields.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an organic EL displaydevice having a greater proportion of light emitting region and highreliability, and enabling use of a large size substrate, fabrication ofa number of elements within a substrate, and reduction of manufacturingcost, and a method for preparing the same.

While several structures for isolating elements (which are designatedelement-isolating structures, hereinafter), including wall structures,cavity structures, trench structures, well structures, inversely taperedstructures, overhang structures and undercut structures were proposed inthe art, the element-isolating structures are always located closer to adepositing material source than the light emitting elements. On thisaccount, when a display device is manufactured in high yields,insulative strips must be given a margin having a width approximatelyequal to the height of the element-isolating structures. However, theprovision of a greater margin leads to narrowing of the light emittingregion, affecting the quality of display. Lowering the height of theelement-isolating structures increases the possibility for the "metalelectrode having a low work function" to cover the element-isolatingstructures, which means that the isolation of elements becomes difficultand hence, the manufacturing yield lowers.

For example, when walls of 4 μm high and 5 μm wide are formed, thesituation is as follows. Since the error of alignment between walls andinsulative strips is approximately 5 μm when a common aligner of thefull exposure type is used, the insulative strips must also have a widthof 5 μm in consideration of a margin. Also, where the "organic layerincluding a light emitting layer" is incident on the substrate from amaximum inclination angle of 45° relative to a direction orthogonal tothe substrate, a margin at least equal to the wall height of 4 μm isnecessary in consideration of the shadowed portion. Accordingly, summingthe margins on both sides of the wall gives the consequence that theinsulative strip must have a width of 23 μm which is the sum of thewidth of the wall and all the margins.

If the gap between adjacent transparent conductive films is 5 μm, in thecase of a high-definition simple matrix display having elements arrangedat a pitch of 100 μm, then (100-23)×(100-5)÷(100×100)=0.7315, indicatingthat the effective light emitting regions are reduced to about 73%.

The problem essentially originates from the fact that element-isolatingstructures extend to a substantial extent from the light emittingsurface toward the incident direction of deposition materials. If it ispossible that a margin be eliminated from the insulative strips and thevariation of the light emitting region at the position of the substratebe eliminated, while maintaining high manufacturing yields, then thelight emitting region can be widened, and as a result, the manufactureof a high illuminance display device can be realized.

Specifically, the above objects are accomplished by the invention of thefollowing construction.

(1) An organic electroluminescent display device comprising a pluralityof organic electroluminescent elements each having at least a firstelectrode, one or more organic layers participating in light emissioncapability, and a second electrode, said elements being able to beindependently electrically operated to emit light,

said device further comprising a groove structure at the boundarybetween two adjacent organic electroluminescent elements for isolatingat least one of the first and second electrodes between said twoadjacent organic electroluminescent elements.

(2) The organic electroluminescent display device of (1) wherein saidgroove structure has a depth which is 1/2 to 20 times the totalthickness of the organic layer and the second electrode layer.

(3) The organic electroluminescent display device of (1) wherein saidgroove structures has an opening and is provided near at least one sideof the opening with an overhang extending generally parallel to asubstrate and toward the center of the groove structure.

(4) The organic electroluminescent display device of (1) wherein saidoverhang is formed near each of opposed sides of the opening of thegroove structure.

(5) The organic electroluminescent display device of (1) wherein saidgroove structure has at its bottom a three-dimensional structureextending orthogonal to a surface of a substrate and having a heightwhich is not higher than the second electrode layer in a light emittingregion.

(6) The organic electroluminescent display device of (5) wherein saidthree-dimensional structure has a width which is greater on the side ofan upper end thereof than on the side of the bottom of said groovestructure.

(7) The organic electroluminescent display device of (1) wherein a sideor opening of said groove structure is at least partially beveled orrounded.

(8) The organic electroluminescent display device of (3) wherein saidoverhang is made of an insulative material and a portion of saidoverhang is formed on the substrate or an underlying layer so as tocover a portion of said first electrode.

(9) The organic electroluminescent display device of (3) wherein saidoverhang is formed at a height of 10 nm to 5 μm above the opening end ofsaid groove structure.

(10) The organic electroluminescent display device of (3) wherein saidoverhang formed on the substrate or an underlying layer has a step oredge which is beveled at an angle of up to 45° relative to a depositionsurface.

(11) The organic electroluminescent display device of (3) wherein aconductive film having a thickness of up to 2 μm is formed on at least apartial region of said overhang.

(12) The organic electroluminescent display device of (1) wherein atleast a portion of said groove structure is formed in an underlyinglayer having any one of a color filter layer, a fluorescence conversionlayer, and an overcoat layer.

(13) A method for preparing an organic electro-luminescent displaydevice comprising the steps of:

forming a groove structure in an insulative substrate or an underlyinglayer on the substrate,

forming a first electrode,

forming at least an organic layer participating in light emissioncapability, and

depositing a second electrode,

wherein the step of depositing a second electrode uses a process havinglow step coverage whereby said second electrode is isolated by theresulting groove structure.

(14) The method for preparing an organic electroluminescent displaydevice of (13) wherein said first electrode, said organic layer and saidsecond electrode are formed by a vapor phase deposition process.

(15) The method for preparing an organic electro-luminescent displaydevice of (13) wherein said second electrode is formed by obliqueevaporation.

(16) The method for preparing an organic electro-luminescent displaydevice of (13), further comprising the step of forming an overhang nearat least one side of an opening of the groove structure during or afterthe step of forming a groove structure, said overhang extendinggenerally parallel to the substrate and toward the center of the groovestructure.

(17) The method for preparing an organic electro-luminescent displaydevice of (13), further comprising the step of forming athree-dimensional structure during the step of forming a groovestructure, said three-dimensional structure extending from a bottom ofsaid groove structure and orthogonal to a surface of the substrate andhaving a height which is not higher than the second electrode layer in alight emitting region.

(18) The method for preparing an organic electro-luminescent displaydevice of (16), wherein said overhang is formed using an insulativematerial, and a portion of said overhang is formed on the substrate orthe underlying layer so as to cover a portion of said first electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmental sectional view of an organic EL display deviceaccording to a first embodiment of the invention.

FIG. 2 is a view similar to FIG. 1, illustrating the deposition of asecond electrode when the incident direction of depositing particles toa substrate is changed from that of FIG. 1.

FIG. 3 is a fragmental sectional view of an organic EL display deviceaccording to a second embodiment of the invention.

FIG. 4 is a fragmental sectional view of an organic EL display deviceaccording to a third embodiment of the invention.

FIG. 5 is a fragmental sectional view of an organic EL display deviceaccording to a fourth embodiment of the invention.

FIG. 6 is a fragmental sectional view of an organic EL display deviceaccording to a fifth embodiment of the invention.

FIG. 7 is a fragmental sectional view of an organic EL display deviceaccording to a sixth embodiment of the invention.

FIG. 8 is a fragmental sectional view of an organic EL display deviceaccording to a seventh embodiment of the invention.

FIG. 9A is a plan view illustrating a manufacturing step in Example 1 ofthe invention, and FIG. 9B is a sectional view taken along lines A-A' inFIG. 9A.

FIG. 10A is a plan view illustrating a manufacturing step in Example 1of the invention, and FIG. 10B is a sectional view taken along linesA-A' in FIG. 10A.

FIG. 11A is a plan view illustrating a manufacturing step in Example 1of the invention, and FIG. 11B is a sectional view taken along linesA-A' in FIG. 11A.

FIG. 12A is a plan view illustrating a manufacturing step in Example 1of the invention, and FIG. 12B is a sectional view taken along linesA-A' in FIG. 12A.

FIG. 13A is a plan view illustrating a manufacturing step in Example 2of the invention, and FIG. 13B is a sectional view taken along linesB-B' in FIG. 13A.

FIG. 14A is a plan view illustrating a manufacturing step in Example 2of the invention, and FIG. 14B is a sectional view taken along linesB-B' in FIG. 14A.

FIG. 15A is a plan view illustrating a manufacturing step in Example 2of the invention, and FIG. 15B is a sectional view taken along linesB-B' in FIG. 15A.

FIG. 16A is a plan view illustrating a manufacturing step in Example 2of the invention, and FIG. 16B is a sectional view taken along linesB-B' in FIG. 16A.

FIG. 17A is a plan view illustrating a manufacturing step in Example 2of the invention, and FIG. 17B is a sectional view taken along linesB-B' in FIG. 17A.

FIG. 18A is a plan view illustrating a manufacturing step in Example 2of the invention, and FIG. 18B is a sectional view taken along linesB-B' in FIG. 18A.

FIG. 19 is a sectional view taken along lines C-C' in FIGS. 18A and 18Billustrating a manufacturing step in Example 2 of the invention.

FIG. 20 is a sectional view illustrating a manufacturing step in Example2 of the invention.

FIG. 21 is a sectional view illustrating a manufacturing step in Example2 of the invention.

FIG. 22 is a sectional view illustrating a manufacturing step in Example3 of the invention.

FIG. 23 is a sectional view illustrating a manufacturing step in Example4 of the invention.

FIG. 24 is a sectional view illustrating a manufacturing step in Example4 of the invention.

FIG. 25 is a sectional view illustrating a manufacturing step in Example4 of the invention.

FIG. 26 is a sectional view illustrating a manufacturing step in Example4 of the invention.

FIG. 27 is a sectional view illustrating a manufacturing step in Example4 of the invention.

FIG. 28 is a sectional view illustrating a manufacturing step in Example4 of the invention.

FIG. 29 is a sectional view illustrating a manufacturing step in Example5 of the invention.

FIG. 30 is a fragmental sectional view illustrating a prior art methodof preparing an organic EL display having walls.

FIG. 31 schematically illustrates the prior art manner of obliqueevaporation.

FIG. 32 is a fragmental sectional view illustrating the depositing stateat position A in FIG. 31.

FIG. 33 is a fragmental sectional view illustrating the depositing stateat position B in FIG. 31.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention solves the problems in the following way.

The basic principle is to configure a element-isolating structure so asnot to extend high above from a substrate. That is, the means forisolating adjacent elements can be realized by forming aelement-isolating structure in which a groove structure isolatesadjacent elements, or a element-isolating structure in which the groovestructure additionally has a structure for facilitating elementisolation. The first electrode elements disposed nearer to the substrateside are formed to cross the grooves or interconnected via anotherconductive film if necessary. At least the portion of the firstelectrode crossing the groove is covered with an insulative film so asto avoid shortcircuiting with the light emitting layer or secondelectrode. After such a structure is formed, an organic layer or layersincluding a light emitting layer are deposited and in sequence, a secondelectrode is formed in such a manner that the element-isolatingstructure may not be fully covered.

This procedure eliminates a need for consideration of a portion shadowedby the element-isolating structure because the majority of the lightemitting region is located nearer to the depositing material source thanthe element-isolating structure. That is, the likelihood that the areaof the light emitting region is reduced by the height and alignmentmargin of the element-isolating structure is minimized.

As in the previous example, if a high definition, simple matrix displayis assumed in which the gap between adjacent transparent conductivestrips is 5 μm, the width of a groove is 5 μm, the margin in forming theinsulative film relative to the groove is 5 μm on one side of thegroove, and elements are arranged at a pitch of 100 μm, then(100-15)×(100-5)÷(100×100)=0.8075, indicating that the effective lightemitting region is increased about 7%. Further, if the insulative filmcovering the grooves is patterned in a self-aligning manner, then(100-5)×(100-5)÷(100×100)=0.9025, indicating that the effective lightemitting region beyond 90% is available.

The organic EL display device includes a plurality of organic ELelements which each have at least a hole injecting electrode, anelectron injecting electrode, and one or more organic layersparticipating in light emission function, and which can be independentlyelectrically operated for light emission, and includes a groovestructure at the boundary between adjacent organic EL elements forisolating at least one of the electrodes between the adjacent organic ELelements.

The means for isolating adjacent elements can be realized by forming aelement-isolating structure in which a groove structure isolatesadjacent elements, or a element-isolating structure in which the groovestructure additionally has a three-dimensional structure forfacilitating element isolation.

That is, the element-isolating structure does not protrude from thedeposition surface or light emitting surface toward the direction inwhich depositing material travels, structural walls and insulativestrips become unnecessary, and a wider effective light emitting regionis available.

The groove structures may be formed directly in a substrate or in anunderlying layer which is formed on the substrate to a predeterminedthickness. The size of groove structure which is sufficient to isolateelements is not critical and may be determined as appropriate inaccordance with the size of a display device, the size of organic ELelements to be isolated, the thickness of the respective layers to bedeposited, depositing methods, and other factors. Illustratively, thegroove structure usually has a width of about 1 to 20 μm, especiallyabout 5 to 10 μm, and a depth which is about 1/2 to 20 times, especiallyabout 2 to 10 times, the total thickness of the organic layer and secondelectrode layer.

The underlying layer is preferably formed using a material which iselectrically insulative, can be etched, and does not interfere with thefirst electrode layer to be deposited thereon. The underlying layer inwhich the groove structure is formed may also be made of an insulativematerial having photosensitivity. Illustrative materials are resinmaterials such as polyimides, acrylic resins, and olefinic resins, andinorganic materials such as SiO₂, SiNx, SiON, Al₂ O₃, and spin-on-glass(SOG) film. The underlying layer may be formed by an appropriate methodwhich is selected from well-known film-forming methods such asevaporation, sputtering, coating, printing and spin coating inaccordance with a particular material used.

The groove structure may be formed as a simple U-shaped recess or arecess diverging toward its opening or inversely, a recess divergingtoward its bottom. The angle of inclination is not critical although itis preferably ±30° to 60°, especially ±45° relative to the openingdirection (or direction orthogonal to the substrate). The groovestructure may be provided near its opening with an overhang extendinggenerally parallel to the substrate and toward the center of the groovestructure or have an additional structure extending from the bottom in adirection orthogonal to the substrate surface (or upright).

The display device having the element-isolating structure can befabricated, for example, as follows.

First, a substrate provided with groove structures is furnished. This isachieved by such methods as a method of indenting grooves in aninsulative substrate, or a method of forming an underlying layer on aninsulative substrate and forming grooves in the underlying layer byphotolithography. Also, an auxiliary conductor to be connected to afirst electrode may be previously formed below the underlying layer.

Next, the first electrode is formed. The first electrode is formed so asto extend across the groove structures and be electrically connected toregions where adjacent elements are to be formed. To this end, the firstelectrode is formed by a process having good step coverage or so as tobe interconnected via the auxiliary conductor formed under theinsulative film beforehand. The first electrode may be patterned byphotolithography or a similar technique.

An insulative layer is formed to cover the first electrode formed in thegroove structure areas. This is because current leakage is likely tooccur between the first electrode and the second electrode in the groovestructure areas. Also when the auxiliary electrode is used, theconnection portions of the first electrode and the auxiliary electrodeis covered with the insulative layer for the same reason. Further, theinsulative film formed on the light emitting region of the firstelectrode is removed by photolithography or a similar technique. Theinsulative film covering the first electrode in the groove structureareas may be patterned so as to cover the edges of the first electrodestrips too, thereby forming a structure capable of suppressing leakagefailure at the strip edges.

After the above-described structure is formed, an organic medium orlayer including a light emitting layer and participating in at leastlight emission function is deposited. Subsequently, a second electrodeis formed by such a method that the groove structure areas may not befully covered. The method of not fully covering the groove structureareas is by setting the opening direction of the groove structure (ordirection orthogonal to the substrate) at a certain angle with respectto the direction in which depositing particles travel. Moreparticularly, in an evaporation or sputtering process, the substrate isinclined such that the substrate surface may form an angle of not equalto 90° with a line connecting the center of an evaporation source ortarget and the center of the substrate. In this case, an obliqueevaporation process featuring less lateral spread or step coverage isespecially preferred. When the direction in which depositing particlestravel is set different from the opening direction of the groovestructure, a shadow area is defined within the groove structure due tothe incident angle of depositing particles and this shadow area becomesan area where no particles are deposited. The incident angle ofdepositing particles relative to the opening direction of the groovestructure is preferably about 10 to 80°, more preferably about 60 to80°.

Where the groove structure is provided near its opening with an overhangextending toward the center of the groove structure or has an additionalstructure extending from the bottom, the direction in which depositingparticles travel may be set identical with the opening direction of thegroove structure.

Further, a metal or insulative film stable to moisture and oxygen may bestacked as a protective film on the second electrode layer.

It is then understood that even when the angle at which the secondelectrode material reaches the substrate largely varies during theprocess, the depositing regions change only within the grooves, and noinfluence is given to the actual light emitting regions. This means thatthe invention has a significant advantage when a display device isfabricated using a large size substrate, because there does not arisethe phenomenon that as seen from FIG. 33 versus FIG. 32 of the prior artexample depicting positions B and A in FIG. 31, the light emittingregion is reduced in size due to a different incident angle ofdepositing particles 41 for the second electrode.

Usually, at least one of the first and second electrodes is formed as alight transmissive film. When the first electrode is a lighttransmissive film, the insulative film in which grooves are formed maybe a color filter or fluorescent filter.

Organic layers including a light emitting layer may be formed by eithera vacuum deposition process or a spin coating process. Understandably,when organic layers are formed by spin coating, the grooves should bedeep enough so that the groove structures are not completely embedded.

When an auxiliary conductor for the first electrode is formed asdemonstrated in Example 2 later, the groove structures can be formedafter the formation of the first electrode. The groove structures aredesirably formed under such conditions that the surface of the auxiliaryconductor is not exposed in the grooves. The auxiliary conductor isdesirably of a layer structure including an inexpensive low resistancemetal material such as aluminum or aluminum base alloy and a stableconductor such as chromium or TiN stacked thereon. The auxiliaryconductor is preferably formed in areas other than the light emittingregions.

When an auxiliary conductor for the second electrode is formed asdemonstrated in Example 3 later, the auxiliary conductor is preferablyformed after the formation of the insulative layer 4. In thisembodiment, the auxiliary conductor for the second electrode is notcompletely covered with the organic layers and thus partially exposedbecause of poor step coverage during deposition of the organic layers.Then, when a second electrode layer is formed thereon, electricalcontact and conduction between the auxiliary conductor and the secondelectrode is provided at the exposed areas. The material of which theauxiliary conductor is made is the same as in the case of the auxiliaryconductor for the first electrode. The auxiliary conductor is preferablyformed in areas other than the light emitting regions, especially on theinsulative layer 4.

Now referring to the drawings, the organic EL display device of thepresent invention is described in further detail.

FIG. 1 is a fragmental sectional view of an organic EL display deviceaccording to a first embodiment of the invention. In the figure, theorganic EL display device of the invention is illustrated as comprisinga substrate 1 of glass or the like which is formed with a groovestructure of rectangular or U shape in cross section, and on which afirst electrode layer 3 and an insulative layer 4 are formed. Theinsulative layer provides insulation between the first electrode layer 3and a second electrode layer for preventing leakage and in theillustrated embodiment, is formed so as to extend to an opening end ofthe groove structure 2. Deposited on the first electrode layer 3 and theinsulative layer 4 is an organic layer 5. On the organic layer 5, asecond electrode layer 6 is formed to the illustrated shape whenfilm-forming or depositing particles 7 travel from the arrow direction.The second electrode layer 6 thus formed leaves a non-deposited regionwithin the groove structure 2 whereby two elements are isolated by thegroove structure 2.

FIG. 2 illustrates a second electrode layer which is deposited as inFIG. 1 when the incident angle of depositing particles 7 is changed. Asseen from the figure, except that the non-deposited region left withinthe groove structure differs in size, the change of the incident angleof depositing particles 7 gives no influence on the remaining portionand thus, does not narrow the light emitting regions of the elements.

FIG. 3 is a fragmental sectional view of an organic EL display deviceaccording to a second embodiment of the invention. In this embodiment,an underlying layer 1a is formed on the substrate 1, and the groovestructure 2 is formed in the underlying layer 1a. The groove structure 2may be formed either by removing a portion of the underlying layer 1a asin the illustrated embodiment or to a depth reaching the substrate 1.The remaining construction is the same as in FIG. 1, and like componentsare designated by the same numerals and their description is omitted.

FIG. 4 is a fragmental sectional view of an organic EL display deviceaccording to a third embodiment of the invention. This embodimentincludes a tapered or beveled edge 22 near an opening of the groovestructure 2. The provision of the tapered edge 22 is effective forpreventing breaks at the edge or thinning of the first electrode andother layers near the opening and current concentration thereat. Thebeveled edge 22 preferably has a bevel angle of about 30 to 60 degrees.The beveled edge 22 may also be formed round or curvilinear and if soformed, the round arc preferably has a radius of curvature of 0.5 to 2μm, especially about 1 μm. The site to be beveled or rounded may be aportion of the side or opening of the groove structure, preferably theopening. The remaining construction is the same as in FIG. 1, and likecomponents are designated by the same numerals and their description isomitted.

FIG. 5 is a fragmental sectional view of an organic EL display deviceaccording to a fourth embodiment of the invention. This embodimentincludes overhangs 8 near the opening of the groove structure 2 whichextend generally parallel to the substrate and toward the center of thegroove structure. The groove structure 2 is formed in the underlyinglayer 1a on the substrate 1. The overhangs 8 are formed like eaves andextend from opposite sides of the opening of the groove structure. Theeaves-like overhangs preferably have a thickness of about 10 nm to about5 μm.

For example, the overhangs 8 can be formed as follows. First, byapplication means having good step coverage such as coating or spincoating, a first layer is formed so as to fill the interior of thegroove structure 2 therewith. The materials for the first layer arepreferably polyimide, SOG film and so on. Then the first layer isremoved except for the portion of the first layer within the groovestructure 2. A second layer which is to form the overhangs 8 is formedthereon while leaving an aperture 21, whereupon the first layer isremoved. The materials for the second layer are preferably resinousmaterials such as resists, polyimides, acrylic resins, and olefinresins, and inorganic materials such as SiO₂, SiNx, SiON, Al₂ O₃, andSOG (spin-on-glass) film. The remaining construction is the same as inFIG. 1, and like components are designated by the same numerals andtheir description is omitted.

FIG. 6 is a fragmental sectional view of an organic EL display deviceaccording to a fifth embodiment of the invention. This embodimentincludes overhangs 8 near the opening of the groove structure 2 whichextend generally parallel to the substrate and toward the center of thegroove structure. The overhangs 8 are tapered such that their lateralextension gradually decreases toward the bottom of the groove structure2. The groove structure 2 is formed in the underlying layer 1a on thesubstrate 1.

In this embodiment, the overhangs 8 are formed, for example, by forminga first layer so as to fill the interior of the groove structure 2therewith, forming a second layer while leaving an aperture 21, andetching away a portion of the first layer under properly selectedconditions. The remaining construction is the same as in FIG. 5, andlike components are designated by the same numerals and theirdescription is omitted.

FIG. 7 is a fragmental sectional view of an organic EL display deviceaccording to a sixth embodiment of the invention. This embodimentincludes an overhang 8 near the opening of the groove structure 2 whichextends generally parallel to the substrate and toward the center of thegroove structure, but from only one side of the opening of the groovestructure 2. The overhang 8 is tapered such that its lateral extensiongradually decreases toward the bottom of the groove structure 2. Thegroove structure 2 is formed in the underlying layer 1a on thesubstrate 1. The remaining construction is the same as in FIG. 6, andlike components are designated by the same numerals and theirdescription is omitted.

FIG. 8 is a fragmental sectional view of an organic EL display deviceaccording to a seventh embodiment of the invention. This embodimentincludes a structure 9 extending from the bottom of the groove structure2 toward the opening thereof. The structure 9 may have an equal sizeboth at the bottom and at the opening or be formed so as to dilatetoward the opening or the bottom. For effective element isolation, thestructure 9 is preferably formed so as to dilate toward the opening. Thestructure 9 preferably has a height at or below the surface on whichelement layers are deposited, especially at or below the secondelectrode layer deposited on areas of the substrate to serve as lightemitting regions. Too high the structure 9 can cause some inconvenientproblems, for example, that an additional nondeposited region in thesecond electrode is left at a position other than the groove structure.The remaining construction is the same as in FIG. 1, and like componentsare designated by the same numerals and their description is omitted.Furthermore, the structure 9 may be a structure having a base on theside of the bottom of the groove structure and an overhang or overhangson the side of the opening which extend generally parallel to thesubstrate surface or dilate in width.

The materials of which the structure is made are preferably the samematerials as the underlying layer and negative working photosensitiveresins. Where the structure has a base and overhangs, the base ispreferably made of polyimides or resists and the overhangs arepreferably made of resists and photosensitive resins such asphotosensitive polyimides.

Next, the organic EL elements of which the organic EL display device ofthe invention is constructed are described.

According to the invention, the organic EL element includes on asubstrate 1 a hole injecting electrode 3 of ITO or the like as the firstelectrode, at least one organic layer 5 participating in light emissioncapability, and an electron injecting electrode 6 as the secondelectrode as shown in FIG. 1, for example. The organic layer may be of aconstruction including a hole injecting and transporting layer, a lightemitting layer, and an electron injecting and transporting layer.Alternatively, an inversely stacked layer construction is employable.

Also acceptable is a construction in which, for example, a first holeinjecting electrode of ITO or the like, a first hole injecting layer, afirst light emitting layer, a first electron injecting layer, and afirst electron injecting electrode are sequentially formed on asubstrate; a second electron injecting layer, a second light emittinglayer, a second hole injecting layer, and a second hole injectingelectrode are sequentially formed thereon; and further a third holeinjecting layer, a third light emitting layer, a third electroninjecting layer, and a second electron injecting electrode aresequentially formed thereon.

Further acceptable is a construction in which, for example, a firstelectron injecting electrode, a first electron injecting layer, a firstlight emitting layer, a first hole injecting layer, and a first holeinjecting electrode are sequentially formed on a substrate; a secondhole injecting layer, a second light emitting layer, a second electroninjecting layer, and a second electron injecting electrode aresequentially formed thereon; and further a third electron injectinglayer, a third light emitting layer, a third hole injecting layer, and asecond hole injecting electrode are sequentially formed thereon. In thisembodiment, the electron injecting electrode or the like is preferablyformed to a thickness of up to 100 nm in order to ensure lighttransmission. The above constructions having plural light emittinglayers are suited for full color light emission and white color lightemission.

A transparent or translucent electrode is preferred as the holeinjecting electrode because the hole injecting electrode is generallyformed as a first electrode on the substrate side and permits emittedlight to exit therethrough. The transparent electrodes include those oftin-doped indium oxide (ITO), zinc-doped indium oxide (IZO), zinc oxide(ZnO), tin oxide (SnO₂), and indium oxide (In₂ O₃), with ITO and IZObeing preferred. The ITO usually contains In₂ O₃ and SnO instoichiometry although the oxygen content may deviate somewhattherefrom.

The hole injecting electrode should have at least a sufficient thicknessfor hole injection and is preferably about 10 to about 500 nm thick,especially about 30 to 300 nm thick. Although no upper limit need beimposed on the thickness of the hole injecting electrode, too thickelectrodes can give rise to problems including peeling, poorworkability, stress failure, low light transmittance and leakage due tosurface roughness. Inversely, a too thin electrode is undesirable infilm strength during manufacture, hole transporting capability, andelectric resistance.

The hole injecting electrode can be formed by evaporation or othertechniques although it is preferably formed by sputtering.

The electron injecting electrode is preferably formed from materialshaving a low work function, for example, metal elements such as K, Li,Na, Mg, La, Ce, Ca, Sr, Ba, Al, Ag, In, Sn, Zn, and Zr, and binary orternary alloys made of two or three such metal elements for stabilityimprovement. Preferred alloys are Ag--Mg (Ag: 1 to 20 at %), Al--Li (Li:0.3 to 14 at %), In--Mg (Mg: 50 to 80 at %), and Al--Ca (Ca: 5 to 20 at%). Alternatively, the electrode may be formed by combining an oxide ofsuch a metal with an auxiliary electrode having good electricalconductivity. It is understood that the electron injecting electrode canbe formed by evaporation or sputtering.

The electron injecting electrode thin film may have at least asufficient thickness for electron injection, for example, a thickness ofat least 0.1 nm, preferably at least 1 nm. Although the upper limit isnot critical, the electrode thickness is typically about 1 to about 500nm. On the electron injecting electrode, an auxiliary electrode may beprovided.

The auxiliary electrode may have at least a sufficient thickness toensure efficient electron injection and prevent the ingress of moisture,oxygen and organic solvents, preferably a thickness of at least 50 nm,more preferably at least 100 nm, most preferably 100 to 1,000 nm. A toothin auxiliary electrode would exert its effect little, lose a stepcoverage capability, and provide insufficient connection to a terminalelectrode. If too thick, greater stresses are generated in the auxiliaryelectrode, accelerating the growth rate of dark spots.

The thickness of the electron injecting electrode and the auxiliaryelectrode combined is usually about 100 to about 1,000 nm though it isnot critical.

After formation of the electrodes, a protective film may be formed inaddition to the auxiliary electrode using inorganic materials such asSiOx, and organic materials such as Teflon and chlorine-containingfluorocarbon polymers. The protective film may be transparent or opaqueand has a thickness of about 50 to 1,200 nm. The protective film may beformed by conventional sputtering, evaporation and PECVD processes aswell as the above-mentioned reactive sputtering process.

Further preferably, a sealing layer may be provided on the element inorder to prevent the organic layers and electrodes thereof fromoxidation. In order to prevent the ingress of moisture, the sealinglayer is formed by attaching a shield plate to the substrate through anadhesive resin layer for sealing. The sealing gas is preferably an inertgas such as argon, helium, and nitrogen. The sealing gas shouldpreferably have a moisture content of less than 100 ppm, more preferablyless than 10 ppm, especially less than 1 ppm. The lower limit of themoisture content is usually about 0.1 ppm though not critical.

The shield plate is preferably selected from flat plates of transparentor translucent materials such as glass, quartz and resins, with glassbeing especially preferred. Of these glass materials, alkali glass ispreferred from the standpoint of cost although other glass compositionssuch as soda lime glass, lead alkali glass, borosilicate glass,aluminosilicate glass, and silica glass are also useful. Of these,plates of soda glass without surface treatment are inexpensive andpreferred for use. Metal plates and plastic plates may also be used asthe shield plate.

A spacer may be used for adjusting the height of the shield plate andholding it at the desired height. The spacer may be formed from resinbeads, silica beads, glass beads, and glass fibers, with the glass beadsbeing especially preferred. Usually the spacer is formed from particleshaving a narrow particle size distribution while the shape of particlesis not critical. Particles of any shape which does not obstruct thespacer function may be used. Preferred particles have an equivalentcircle diameter of about 1 to 20 μm, more preferably about 1 to 10 μm,most preferably about 2 to 8 μm. Particles of such diameter shouldpreferably have a length of less than about 100 μm, with the lower limitof length being usually equal to or greater than the diameter though notcritical.

When the shield plate is provided with a recess, the spacer may be usedor not. When used, the spacer should preferably have a diameter in theabove-described range, especially 2 to 8 μm.

The spacer may be premixed in a sealing adhesive or mixed with a sealingadhesive at the time of bonding. The content of the spacer in thesealing adhesive is preferably 0.01 to 30% by weight, more preferably0.1 to 5% by weight.

Any of adhesives which can maintain stable bond strength and gastightness may be used although UV curable epoxy resin adhesives ofcation curing type are preferred.

The substrate material is not critical and may be properly selected inaccordance with the material of electrodes in an organic EL structure tobe stacked thereon. For example, metal materials such as aluminum, andtransparent or translucent materials such as glass, quartz and resinsmay be used. Opaque materials are also acceptable and in this case,ceramics such as alumina, metal sheets of stainless steel or the likewhich have been surface-oxidized or otherwise insulation treated,thermosetting resins such as phenolic resins, and thermoplastic resinssuch as polycarbonates may be used.

Next, the organic material layers included in the organic EL elementsare described.

The light emitting layer has the functions of injecting holes andelectrons, transporting them, and recombining holes and electrons tocreate excitons. It is preferred that relatively electronically neutralcompounds be used in the light emitting layer.

The hole injecting and transporting layer has the functions offacilitating injection of holes from the hole injecting electrode,transporting holes stably, and obstructing electron transportation. Theelectron injecting and transporting layer has the functions offacilitating injection of electrons from the electron injectingelectrode, transporting electrons stably, and obstructing holetransportation. These layers are effective for increasing the number ofholes and electrons injected into the light emitting layer and confiningholes and electrons therein for optimizing the recombination region toimprove light emission efficiency.

The thicknesses of the light emitting layer, the hole injecting andtransporting layer, and the electron injecting and transporting layerare not critical and vary with a particular formation technique althoughtheir thickness is usually preferred to range from about 5 nm to about500 nm, especially about 10 nm to about 300 nm.

The thickness of the hole injecting and transporting layer and theelectron injecting and transporting layer is equal to or ranges fromabout 1/10 times to about 10 times the thickness of the light emittinglayer although it depends on the design of a recombination/lightemitting region. When the electron or hole injecting and transportinglayer is divided into an injecting layer and a transporting layer,preferably the injecting layer is at least 1 nm thick and thetransporting layer is at least 1 nm thick. The upper limit of thicknessis usually about 500 nm for the injecting layer and about 500 nm for thetransporting layer. The same film thickness applies when twoinjecting/transporting layers are provided.

The light emitting layer of the organic EL element contains afluorescent material that is a compound having a light emittingcapability. The fluorescent material may be at least one member selectedfrom compounds as disclosed, for example, in JP-A 264692/1988, such asquinacridone, rubrene, and styryl dyes. Also, quinoline derivatives suchas metal complex dyes having 8-quinolinol or a derivative thereof as theligand such as tris(8-quinolinolato)aluminum are included as well astetraphenylbutadiene, anthracene, perylene, coronene, and12-phthaloperinone derivatives. Further useful are the phenylanthracenederivatives described in JP-A 12600/1996 (Japanese Patent ApplicationNo. 110569/1994) and the tetraarylethene derivatives described in JP-A12969/1996 (Japanese Patent Application No. 114456/1994).

It is preferred to use such a compound in combination with a hostmaterial capable of light emission by itself, that is, to use thecompound as a dopant. In this embodiment, the content of the compound inthe light emitting layer is preferably 0.01 to 10% by weight, especially0.1 to 5% by weight. By using the compound in combination with the hostmaterial, the light emission wavelength of the host material can bealtered, allowing light emission to be shifted to a longer wavelengthand improving the luminous efficacy and stability of the element.

As the host material, quinolinolato complexes are preferable, withaluminum complexes having 8-quinolinol or a derivative thereof as theligand being more preferable. These aluminum complexes are disclosed inJP-A 264692/1988, 255190/1991, 70733/1993, 258859/1993 and 215874/1994.

Illustrative examples include tris(8-quinolinolato)aluminum,bis(8-quinolinolato)magnesium, bis(benzo{f}-8-quinolinolato)zinc,bis(2-methyl-8-quinolinolato)aluminum oxide,tris(8-quinolinolato)indium, tris(5-methyl-8-quinolinolato)aluminum,8-quinolinolatolithium, tris(5-chloro-8-quinolinolato)gallium,bis(5-chloro-8-quinolinolato)calcium,5,7-dichloro-8-quinolinolatoaluminum,tris(5,7-dibromo-8-hydroxyquinolinolato)aluminum, andpoly[zinc(II)-bis(8-hydroxy-5-quinolinyl)methane].

Also useful are aluminum complexes having another ligand in addition to8-quinolinol or a derivative thereof. Examples includebis(2-methyl-8-quinolinolato)(phenolato)aluminum(III),bis(2-methyl-8-quinolinolato)(orthocresolato)aluminum(III),bis(2-methyl-8-quinolinolato)(metacresolato)aluminum(III),bis(2-methyl-8-quinolinolato)(paracresolato)aluminum(III),bis(2-methyl-8-quinolinolato)(ortho-phenylphenolato)aluminum(III),bis(2-methyl-8-quinolinolato)(meta-phenylphenolato)aluminum(III),bis(2-methyl-8-quinolinolato)(para-phenylphenolato)aluminum(III),bis(2-methyl-8-quinolinolato)(2,3-dimethylphenolato)aluminum(III),bis(2-methyl-8-quinolinolato)(2,6-dimethylphenolato)aluminum(III),bis(2-methyl-8-quinolinolato)(3,4-dimethylphenolato)aluminum(III),bis(2-methyl-8-quinolinolato)(3,5-dimethylphenolato)aluminum(III),bis(2-methyl-8-quinolinolato)(3,5-di-tert-butylphenolato)aluminum(III),bis(2-methyl-8-quinolinolato)(2,6-diphenylphenolato)aluminum(III),bis(2-methyl-8-quinolinolato)(2,4,6-triphenylphenolato)aluminum(III),bis(2-methyl-8-quinolinolato)(2,3,6-trimethylphenolato)aluminum(III),bis(2-methyl-8-quinolinolato)(2,3,5,6-tetramethylphenolato)aluminum(III),bis(2-methyl-8-quinolinolato)(1-naphtholato)aluminum(III),bis(2-methyl-8-quinolinolato)(2-naphtholato)aluminum(III),bis(2,4-dimethyl-8-quinolinolato)(orthophenylphenolato)aluminum(III),bis(2,4-dimethyl-8-quinolinolato)(para-phenylphenolato)aluminum(III),bis(2,4-dimethyl-8-quinolinolato)(meta-phenylphenolato)aluminum(III),bis(2,4-dimethyl-8-quinolinolato)(3,5-dimethylphenolato)aluminum(III),bis(2,4-dimethyl-8-quinolinolato)(3,5-di-tert-butylphenolato)aluminum(III),bis(2-methyl-4-ethyl-8-quinolinolato)(para-cresolato)aluminum(III),bis(2-methyl-4-methoxy-8-quinolinolato)(paraphenylphenolato)aluminum(III),bis(2-methyl-5-cyano-8-quinolinolato)(ortho-cresolato)aluminum(III), andbis(2-methyl-6-trifluoromethyl-8-quinolinolato)(2-naphtholato)aluminum(III).

Also acceptable arebis(2-methyl-8-quinolinolato)aluminum(III)-μ-oxo-bis(2-methyl-8-quinolinolato)aluminum(III)-μ-oxo-bis(2-methyl-8-quinolinolato)aluminum (III),bis(2,4-dimethyl-8-quinolinolato)aluminum(III)-8-oxo-bis(2,4-dimethyl-8-quinolinolato)aluminum(III)-μ-oxo-bis(2,4-dimethyl-8-quinolinolato)aluminum(III),bis(4-ethyl-2-methyl-8-quinolinolato)aluminum(III),bis(2-methyl-4-methoxyquinolinolato)aluminum(III)-μ-oxo-bis(2-methyl-4-methoxyquinolinolato)aluminum(III),bis(5-cyano-2-methyl-8-quinolinolato)aluminum(III)-μ-oxo-bis(5-cyano-2-methyl-8-quinolinolato)aluminum(III),andbis(2-methyl-5-trifluoromethyl-8-quinolinolato)aluminum(III)-μ-oxo-bis(2-methyl-5-trifluoromethyl-8-quinolinolato)aluminum(III).

Other useful host materials are the phenylanthracene derivativesdescribed in JP-A 12600/1996 (Japanese Patent Application No.110569/1994) and the tetraarylethene derivatives described in JP-A12969/1996 (Japanese Patent Application No. 114456/1994).

The light emitting layer may also serve as the electron injecting andtransporting layer. In this case, tris(8-quinolinolato)aluminum etc. arepreferably used. These fluorescent materials may be evaporated.

Also, if necessary, the light emitting layer may also be a layer of amixture of at least one hole injecting and transporting compound and atleast one electron injecting and transporting compound, in which adopant is preferably contained. In such a mix layer, the content of thedopant is preferably 0.01 to 20% by weight, especially 0.1 to 15% byweight.

In the mix layer, carrier hopping conduction paths are created, allowingcarriers to move through a polarly predominant material while injectionof carriers of opposite polarity is rather inhibited, and the organiccompound becomes less susceptible to damage, resulting in the advantageof an extended device life. By incorporating the aforementioned dopantin such a mix layer, the light emission wavelength the mix layer itselfpossesses can be altered, allowing light emission to be shifted to alonger wavelength and improving the luminous intensity and stability ofthe elements.

The hole injecting and transporting compound and electron injecting andtransporting compound used in the mix layer may be selected fromcompounds for the hole injecting and transporting layer and compoundsfor the electron injecting and transporting layer to be described later,respectively. Inter alia, the compound for the hole injecting andtransporting layer is preferably selected from amine derivatives havingstrong fluorescence, for example, triphenyldiamine derivatives which arehole transporting materials, styrylamine derivatives and aminederivatives having an aromatic fused ring.

The electron injecting and transporting compound is preferably selectedfrom quinoline derivatives and metal complexes having 8-quinolinol or aderivative thereof as a ligand, especially tris(8-quinolinolato)aluminum(Alq3). The aforementioned phenylanthracene derivatives andtetraarylethene derivatives are also preferable.

The mix ratio is preferably determined in accordance with the carrierdensity and carrier mobility. It is usually preferred that the weightratio of the hole injecting and transporting compound to the electroninjecting and transporting compound range from about 1/99 to about 99/1,more preferably from about 10/90 to about 90/10, especially from about20/80 to about 80/20.

Also preferably, the thickness of the mix layer ranges from thethickness of a mono-molecular layer to less than the thickness of theorganic compound layer, specifically from 1 to 85 nm, more preferably 5to 60 nm, especially 5 to 50 nm.

Preferably the mix layer is formed by a co-deposition process ofevaporating the compounds from distinct sources. If both the compoundshave approximately equal or very close vapor pressures or evaporationtemperatures, they may be pre-mixed in a common evaporation boat, fromwhich they are evaporated together. The mix layer is preferably auniform mixture of both the compounds although the compounds can bepresent in island form. The light emitting layer is generally formed toa predetermined thickness by evaporating an organic fluorescent materialor coating a dispersion thereof in a resin binder.

In the hole injecting and transporting layer, there may be used variousorganic compounds as described, for example, in JP-A 295695/1988,191694/1990, 792/1991, 234681/1993, 239455/1993, 299174/1993,126225/1995, 126226/1995, and 100172/1996, and EP 0650955A1. Exemplaryare tetraaryl-benzidine compounds (triaryldiamines or triphenyldiamines:TPD), aromatic tertiary amines, hydrazone derivatives, carbazolederivatives, triazole derivatives, imidazole derivatives, oxadiazolederivatives having an amino group, and polythiophenes. Two or more ofthese compounds may be used, and on such combined use, they may beformed as separate layers or mixed.

Where the hole injecting and transporting layer is formed separately asa hole injecting layer and a hole transporting layer, two or morecompounds are selected in a proper combination from the compoundscommonly used in hole injecting and transporting layers. In this regard,it is preferred to laminate layers in such an order that a layer of acompound having a lower ionization potential may be disposed adjacentthe hole injecting electrode (ITO). It is also preferred to use acompound having good thin film forming ability at the hole injectingelectrode surface. The order of lamination also applies where aplurality of hole injecting and transporting layers are provided. Suchan order of lamination is effective for lowering the drive voltage andpreventing current leakage and the development and growth of dark spots.Since evaporation is utilized in the manufacture of devices, films asthin as about 1 to 10 nm can be formed uniform and pinhole-free, whichrestrains any change in color tone of light emission and a drop ofefficiency by re-absorption even if a compound having a low ionizationpotential and absorption in the visible range is used in the holeinjecting layer. Like the light emitting layer, the hole injecting andtransporting layer may be formed by evaporating the above-mentionedcompounds.

In the electron injecting and transporting layer which is optionallyprovided, there may be used quinoline derivatives including organicmetal complexes having 8-quinolinol or a derivative thereof as a ligandsuch as tris(8-quinolinolato)aluminum (Alq3), oxadiazole derivatives,perylene derivatives, pyridine derivatives, pyrimidine derivatives,quinoxaline derivatives, diphenylquinone derivatives, andnitro-substituted fluorene derivatives. The electron injecting andtransporting layer can also serve as the light emitting layer. In thiscase, use of tris(8-quinolinolato)aluminum etc. is preferred. Like thelight emitting layer, the electron injecting and transporting layer maybe formed by evaporation or the like.

Where the electron injecting and transporting layer is formed separatelyas an electron injecting layer and an electron transporting layer, twoor more compounds are selected in a proper combination from thecompounds commonly used in electron injecting and transporting layers.In this regard, it is preferred to stack layers in such an order that alayer of a compound having a greater electron affinity may be disposedadjacent the electron injecting electrode. The order of stacking alsoapplies where a plurality of electron injecting and transporting layersare provided.

Of the above-mentioned organic layers, the hole injecting andtransporting layer, electron injecting and transporting layer and otherlayers may be formed of inorganic materials.

In forming the hole injecting and transporting layer, the light emittinglayer, and the electron injecting and transporting layer, vacuumevaporation is preferably used because homogeneous thin films areavailable. By utilizing vacuum evaporation, there is obtained ahomogeneous thin film which is amorphous or has a crystal grain size ofup to 0.2 μm, especially up to 0.1 μm. If the grain size is more than0.2 μm, especially more than 0.1 μm, uneven light emission would takeplace and the drive voltage of the device must be increased with asubstantial drop of hole injection efficiency.

The conditions for vacuum evaporation are not critical although a vacuumof 10⁻⁴ Pa or lower and a deposition rate of about 0.01 to 1 nm/sec. arepreferred. It is preferred to successively form layers in vacuum becausethe successive formation in vacuum can avoid adsorption of impurities onthe interface between the layers, thus ensuring better performance.Also, the drive voltage of elements can be reduced and the developmentand growth of dark spots be restrained.

In the embodiment wherein the respective layers are formed by vacuumevaporation, where it is desired for a single layer to contain two ormore compounds, boats having the compounds received therein areindividually temperature controlled to achieve co-deposition.

The substrate may be provided with a color filter film, a fluorescentmaterial-containing color conversion film or a dielectric reflectingfilm for controlling the color of light emission.

The use of the color filter film, fluorescent material-containing colorconversion film or dielectric reflecting film as the underlying layerreduces the number of steps because the step of forming the underlyinglayer in which the groove structure is to be formed can be omitted.

The color filter film used herein may be a color filter as used inliquid crystal displays and the like. The properties of a color filtermay be adjusted in accordance with the light emission of the organic ELelements so as to optimize the extraction efficiency and color purity.

It is also preferred to use a color filter capable of cutting externallight of short wavelength which is otherwise absorbed by the EL elementsmaterials and fluorescence conversion layer, because the lightresistance and display contrast of the elements are improved.

An optical thin film such as a multilayer dielectric film may be usedinstead of the color filter.

The fluorescence conversion filter film is to convert the color of lightemission by absorbing electro-luminescence and allowing the fluorescentmaterial in the film to emit light. It is formed from three components:a binder, a fluorescent material, and a light absorbing material.

The fluorescent material used may basically have a high fluorescentquantum yield and desirably exhibits strong absorption in theelectroluminescent wavelength region. In practice, laser dyes areappropriate. Use may be made of rhodamine compounds, perylene compounds,cyanine compounds, phthalocyanine compounds (includingsub-phthalocyanines), naphthalimide compounds, fused ring hydrocarboncompounds, fused heterocyclic compounds, styryl compounds, and coumarincompounds.

The binder is generally selected from materials which do not causeextinction of fluorescence, preferably those materials which can befinely patterned by photolithography or printing technique. Also, thosematerials which are not damaged during deposition of ITO or IZO arepreferable.

The light absorbing material is used when the light absorption of thefluorescent material is short and may be omitted if unnecessary. Thelight absorbing material may also be selected from materials which donot cause extinction of fluorescence of the fluorescent material.

When the color filter film, fluorescent material-containing colorconversion film or dielectric reflecting film is formed, it is preferredto form an overcoat layer thereon. The overcoat layer is effective foraccommodating irregularities of the color filter film, fluorescentmaterial-containing color conversion film or dielectric reflecting film,thereby presenting a smooth surface to ensure the function of theorganic EL elements and preventing the quality of display fromdeteriorating. The materials of which the overcoat layer is made includeresin materials such as polyimides, acrylic resins, and olefinic resins,and SOG (spin-on-glass) and analogous materials which can be formed bycoating liquid raw materials.

The overcoat layer is generally formed by coating, spin coating or thelike. The overcoat layer is formed directly on the substrate toaccommodate irregularities on the substrate surface and may serve as theunderlying layer as does the color filter film, fluorescentmaterial-containing color conversion film or dielectric reflecting film.

After the color filter film, fluorescent material-containing colorconversion film or dielectric reflecting film and the overcoat layer areformed, an inorganic barrier layer may be further formed on theselayers. The inorganic barrier layer is effective for preventing ingressof moisture into the organic EL elements from the color filter film,fluorescent material-containing color conversion film or dielectricreflecting film, thereby ensuring the function of the organic ELelements. Illustrative examples are inorganic materials such as SiO₂,SiNx, SiON, Al₂ O₃ and SOG (spin-on-glass) film.

The organic EL device is of the dc or pulse drive type while it can beof the ac drive type. The applied voltage is generally about 2 to 30volts.

EXAMPLE

Preferred examples of the invention are given below by way ofillustration.

Example 1

As shown in FIGS. 9A and 9B, by an atmospheric pressure CVD process,SiO₂ was deposited 0.9 μm on a glass substrate as an insulative film forforming grooves. FIG. 9A is a plan view and FIG. 9B is a view (only aportion depicted) taken along line A-A' in FIG. 9A (the same appliesdown to FIGS. 13A and 13B). Then, a stripe resist pattern having a linewidth of 145 μm and a gap width of 3 μm was formed by photolithography,and the SiO₂ was etched about 0.9 μm by a reactive ion etching (RIE)process. The etching conditions included an RF power of 2 W/cm², CF₄ =80sccm, and a gas pressure of 100 mTorr (13.3 Pa). Etching was furthercarried out under such conditions that the resist was also etched: an RFpower of 2 W/cm², CF₄ /O₂ =70/30 sccm, and a gas pressure of 100 mTorr(13.3 Pa). At this point, since the SiO₂ was etched while the resistpattern was contracted, a pattern with beveled edges 2a was formed asshown in FIGS. 9A and 9B. The depth of grooves 2 was about three timesthe total thickness of organic layers including a light emitting layerand a second electrode layer to be deposited later.

Next, as shown in FIGS. 10A and 10B, tin-doped indium oxide (ITO) wasdeposited 100 nm as a first electrode layer 3 by a sputtering process.In general, the sputtering process can effect film deposition under goodstep coverage conditions. By setting a gas pressure of 0.3 Pa and asputtering target-to-substrate distance of 120 mm during sputtering, ITOcan be deposited even within the groove structure 2. The ITO waspatterned by photolithography into strips extending approximatelyorthogonal to the strips of SiO₂. Etching was carried out with anetchant of HCl:HNO₃ :H₂ O in a mix ratio of 6:1:19. The resist waspeeled off, obtaining a pattern as shown in FIG. 10A.

Next, as shown in FIGS. 11A and 11B, an SiO₂ insulative layer 4 of 0.3μm thick was formed by an atmospheric CVD process. A resist pattern wasformed so that resist steps might have a bevel angle of about 20°,etching was effected by the RIE process under conditions, an RF power of2 W/cm², CF₄ /O₂ =70/30 sccm, and a gas pressure of 100 mTorr (13.3 Pa),and the resist was peeled off, obtaining a pattern as shown in FIG. 11A.

Next, as shown in FIG. 12B, organic layers 5 including a light emittinglayer were deposited by an evaporation process. While the substrate wasbeing rotated,N,N'-bis(m-methylphenyl)-N,N'-diphenyl-1,1'-bis(methenyphyl-4,4'-diamine(abbreviated as TPD, hereinafter) was first deposited as a holeinjecting layer and a hole transporting layer, andtris(8-hydroxyquinoline)aluminum (abbreviated as Alq3, hereinafter) wasthen deposited as a light emitting layer/electron transporting layer.These layers had a thickness of 50 nm and 50 nm, respectively. It isnoted that the organic layers were formed over the entire surface andthe respective layers are depicted in an integral form in FIG. 12A.

Further in succession, with the vacuum kept, an Mg/Ag alloy (weightratio 10/1) was evaporated as a second electrode 6 as shown in FIGS. 13Aand 13B. The electrode had a thickness of 200 nm. The second electrodewas formed by oblique evaporation from a direction approximatelyorthogonal to the longitudinal direction of the grooves without rotatingthe substrate, so that the grooves were not fully covered. The secondelectrode 6 was formed as separate strips isolated by the groovestructures 2 as shown in FIG. 13A.

As understood from the spirit of the invention, the invention is notlimited to the organic EL element constituting layers and the order ofstacking used in this Example. Other materials may be used for the holeinjecting layer, light emitting layer and second electrode. Also, amultilayer structure may be constructed by further forming a holeinjecting layer, electron transporting layer and electron injectinglayer. Differently stated, the invention is applicable independent ofthe type of material deposited and the structure. Further, an organiclight emitting material which can form a film by coating, typicallypolyphenylene vinylene (PPV) can be used if grooves of a sufficientdepth are formed, although the grooves become shallow as the grooves arepartially filled due to the flow of the material. Since a coating of thecoating type material generally has a thickness of about 100 nm, agroove depth of at least 500 nm is sufficient.

Example 2

This example illustrates the fabrication of a full color display havinga diagonal length of 5 inches and a dot number of 640×480×RGB. The sizeof one dot was as small as 55 μm×165 μm. If element-isolating structuresprotruding from the surface of a substrate on which elements are to beformed are used, the effective light emitting regions are extremelyreduced. The present invention is quite effective when such a finedefinition is required.

First, as shown in FIGS. 14A and 14B, on a clean transparent glasssubstrate, Al--Sc (depicted at 11b) and Cr (depicted at 11a) werecontinuously deposited to a thickness etching process, forming auxiliaryconductor strips 11. It is noted that FIG. 14A is a plan view and FIG.14B is a view (only a portion depicted) taken along line B-B' in FIG.14A (the same applies down to FIGS. 18A and 18B).

Subsequently, as shown in FIGS. 15A and 15B, RED, GREEN, and BLUE colorfilter layers 12a, 12b, and 12c of the pigment dispersion type were eachformed to a thickness of 2.0 μm. These layers, each composed of apigment dispersed in an acrylic resin, were formed by repeating for eachcolor a process including spin coating a commercially available chemicalsolution, pre-baking, exposure, development and curing.

Further, as shown in FIGS. 16A and 16B, to flatten the surface of thecolor filter layers 12a, 12b and 12c, a colorless transparent overcoatlayer 1b also of an acrylic resin was formed in the same manner as thecolor filter layers 12a, 12b and 12c. These layers were formed withcontact holes 13, through which a first electrode 3 to be subsequentlyformed could be interconnected to the auxiliary conductor strips 11.

Next, as shown in FIGS. 17A and 17B, ITO was deposited as a firstelectrode 3 as in Example 1. The ITO was positioned so as to beinterconnected to the auxiliary conductor strips 11 through the contactholes 13 as described just above. The ITO elements for respectiveelements were patterned like islands as shown in FIG. 17A.

Further, as shown in FIGS. 18A, 18B, and 19, SiO₂ was deposited 300 nmas an insulative layer 4 by sputtering and patterned so as to be left inthe contact holes and on opposite sides of areas where grooves were tobe formed. It is noted that FIG. 19 is a cross section taken along lineC-C' in FIG. 18A. Etching of SiO₂ was carried out by a dry etchingprocess so that pattern edges might have a bevel angle of 10° to 30° asshown in FIGS. 18A, 18B, and 19. The etching conditions included an RFpower of 2 W/cm², CF₄ /O₂ =80/20 sccm, a gas pressure of 100 mTorr (13.3Pa), and a time of 2 minutes. The surface of ITO and the surface of theovercoat film were exposed within the element areas.

Subsequently, with the vacuum kept, ashing was carried out for 2 minutesat an RF power of 2 W/cm², O₂ =100 sccm, a gas pressure of 500 mTorr(66.7 Pa). Since the exposed overcoat film was also ashed away at thispoint along with the photoresist as shown in FIG. 20, groove structures2 having not only grooves, but undercuts below the insulative layer 4were formed. The formation of undercuts in this way enables toelectrically isolate adjacent second electrode elements, independent ofthe incident direction to the substrate of the second electrode materialor inter-connecting material to be subsequently deposited. Also, tomitigate leakage failure at steps of ITO, a structure in which steps ofITO were covered with the insulative layer 4 was simultaneously employedin this example. This eliminates a need for an extra step of coveringsteps of ITO with a new insulative film.

For color imaging, the light emitting elements were constructed bydepositing the following materials. In this example, EL materialscapable of white color light emission were used.

Poly(thiophene-2,5-diyl) was deposited to a thickness of 10 nm as a holeinjecting layer, and TPD doped with 1 wt % of rubrene was co-evaporatedto 5 nm as a hole transporting layer/yellow light emitting layer. Anappropriate concentration of rubrene is about 0.1 to about 10% by weightbecause high efficiency light emission occurs at this concentration. Theconcentration may be determined in accordance with a color balance ofemitted light and is governed by the light intensity and wavelengthspectrum of a blue light emitting layer to be subsequently deposited.Then, 4,4'-bis[(1,1,2-triphenyl)ethenyl]biphenyl was deposited 50 nm asa blue light emitting layer, and Alq3 was deposited 10 nm as an electrontransporting layer, completing an organic layer 5.

Next, with the vacuum kept, Al--Li alloy and Al were deposited as asecond electrode 6 by sputtering. As shown in FIG. 21, even on use of aprocess having relatively good step coverage such as sputtering, thesecond electrode elements 6 could be isolated from each other when thegroove structures 2 were provided with undercuts.

Finally, a glass plate was joined in a dry nitrogen atmosphere forsealing, completing a display panel.

The thus fabricated display panel was confirmed to produce a brightdisplay and be highly reliable because of deposition without vacuumbreakage. With this construction and method, not only second electrodeelements in strip form, but second electrode elements in winding formcan also be isolated.

Example 3

In Example 2, after the insulative layer 4 of SiO₂ was formed, Al wassuccessively deposited to 1,500 nm as an auxiliary electrode 15 for thesecond electrode. A resist pattern was formed and Al was etched with amixture of phosphoric acid, nitric acid and acetic acid heated at 45° C.In this step, etching was continued for a so long time that aluminum wassmaller 2 μm than the resist pattern on each side. As in Example 2, SiO₂was etched, and grooves with undercuts were formed by ashing. In thisway, as shown in FIG. 22, the pattern of auxiliary electrode elements 15of Al which was next smaller than the SiO₂ pattern was formed in aself-aligning manner.

Further, yet as in Example 2, an organic layer 5 including a lightemitting layer was formed, and a second electrode 6 was deposited 70 nmby sputtering. As shown in FIG. 22, since the auxiliary electrodeelements 15 formed on the insulative layer 4 of SiO₂ had steps ofapproximately 90°, the organic layer 5 could not fully cover it, and asa consequence, electrical conduction was established between theauxiliary electrode elements 15 and the second electrode elements 6.

Although the second electrode 6 was so thin that its electricalresistance was not fully low, the auxiliary electrode 15 prevented avoltage drop, enabling imaging with minimal variation over the entirescreen.

Example 4

As shown in FIG. 23, a yellow color filter 12d of 2 μm thick was coatedon a glass substrate 1 and patterned so as to define a groove structure2. Then, as shown in FIG. 24, ITO was deposited and patterned as a firstelectrode 3. Further, as shown in FIG. 25, SiO₂ was deposited on the ITOand patterned as an insulative layer 4.

Next, as shown in FIG. 26, polyimide was coated 1 μm and dried for onehour at 120° C. as a structure base 9a. Further, as shown in FIG. 27, anegative resist was coated 1 μm and dried as a structure overhang 9b.Upon exposure from the substrate 1 side, only the portion of the resistwithin the groove structure 2 was exposed. Upon development, aelement-isolating structure 9 having an overhang 9b was formed withinthe groove structure 2 as shown in FIG. 28.

Example 5

As in Example 4, the successive patterns including the insulative layer4 were formed. Next, a positive resist was coated and dried. Afterexposure was made through a mask covering the groove structure 2,exposure was also made from the rear side, followed by development. Thegroove structure 2 having overhangs 8 was formed as shown in FIG. 29because the bevel walls of the groove structure 2 shielded UV radiation.

As seen from the foregoing Examples, the present invention enablesfabrication of organic EL display devices having a larger light emittingsurface area and high reliability. The number of manufacturing steps canbe reduced as best shown in Example 2, achieving a cost reduction.

According to the invention, organic EL display devices having a largerproportion of light emitting region and high reliability, and enablinguse of large sized substrates, fabrication of more elements within asingle substrate, and cost effective manufacture are provided as well asthe method for manufacturing the same.

What is claimed is:
 1. An organic electroluminescent display devicecomprising a substrate having a plurality of organic electroluminescentelements each having at least a first electrode, one or more organiclayers participating in light emission capability, and a secondelectrode, said elements being able to be independently electricallyoperated to emit light, said device further comprising a groovestructure extending into substrate or an underlying layer at theboundary between two adjacent organic electroluminescent elements forisolating at least one of the first and second electrodes between saidtwo adjacent organic electroluminescent elements.
 2. The organicelectroluminescent display device of claim 1 wherein said groovestructure has a depth which is 1/2 to 20 times the total thickness ofthe organic layer and the second electrode layer.
 3. The organicelectroluminescent display device of claim 1 wherein each of said groovestructures has an opening and is provided near at least one side of theopening with an overhang extending generally parallel to the substrateand toward the center of the groove structure.
 4. The organicelectroluminescent display device of claim 3 wherein said overhang isformed near each of opposed sides of the opening of the groovestructure.
 5. The organic electroluminescent display device of claim 3wherein said overhang is made of an insulative material and a portion ofsaid overhang is formed on the substrate or the underlying layer so asto cover a portion of said first electrode.
 6. The organicelectroluminescent display device of claim 3 wherein said overhang isformed at a height of 10 nm to 5 μm above the opening end of said groovestructure.
 7. The organic electroluminescent display device of claim 3wherein said overhang formed on the substrate or the underlying layerhas a step or edge which is beveled at an angle of up to 45° relative toa deposition surface.
 8. The organic electroluminescent display deviceof claim 3 wherein a conductive film having a thickness of up to 2 μm isformed on at least a partial region of said overhang.
 9. The organicelectroluminescent display device of claim 1 wherein said groovestructure has at its bottom a three-dimensional structure extendingorthogonal to a surface of the substrate and having a height which isnot higher than the second electrode layer in a light emitting region.10. The organic electroluminescent display device of claim 9 whereinsaid three-dimensional structure has a width which is greater on theside of an upper end thereof than on the side of the bottom of saidgroove structure.
 11. The organic electroluminescent display device ofclaim 1 wherein a side or opening of said groove structure is at leastpartially beveled or rounded.
 12. The organic electroluminescent displaydevice of claim 1 wherein at least a portion of said groove structure isformed in the underlying layer having any one of a color filter layer, afluorescence conversion layer, and an overcoat layer.